Tar spot (Myrothecium roridum Tode Ex fr.)

Introduction

The disease was first reported in mulberry by Heming et al. (1988) from Suzhou Sericulture Institute, China and Govindaiah et al. (1989) from India. The disease appears in the form of large irregular, circular or linear black spots on the leaves . The disease cause huge loss in severe condition. It is most prevalent in the mulberry growing areas of West Bengal and north Eastern states in India especially during the rainy season with warm temperature and high humidity.

Symptoms

 The spots are circular at first enlarging progressively and become irregular in the later stages especially under extensive moist condition. The vein tissues are included in the necrosis. The circular spots vary in size up to 2 cm dia., occasionally centre of the lesion cracks irregularly and rupture. 

Causal agent

Myrothecium roridum (Tode Ex fr.)

Systematic position

Pathogen description

            Sporodochia on leaf are sessile and polymorphic in surface view, Spore mat wet when young, shinny, black, convex surrounded by a fringe of entangled white hyphae. Marginal hyphae contorted, hyaline usually tapering towards a blunt apex, branched septate cells 20-30x 1-2.2µ. No external mycelium found on plant material. Conidiophore arises directly from the mycelium. Conidiophore hyaline, cylindrical, branched below and then in to 2-3 branches bearing phialides, cosely compacted to form a sub-hymeneal layer septate, cells 6.3-23 ( 14.7) x 1.4-3.6 (1.9) µ (Fig.6). Phialids in whorls of 2-5 at the apex of conidiophores branches, mostly cylindrical, hyaline, some dilute olivaceous, 9-27 (14.2) x 0.9-1.8 91.4)  µ, closely compacted in to parallel rows forming a dens hymeneal layer. Spores rod shaped ends rounded, one end rarely slightly truncate, smooth walled, hyaline to olivaceous, black in mass, guttulate, 4.5-10.8 (7.2) x 1.3-2.7 (1.8) µ (Fig. 5). Sporulation in culture often in concentric zones and consists of small group of conidiopores (Fig. 4), formimg rudimentary sporodochia. The fungus grows well in potato dextrose agar medium with excellent sporulation.           

Pre disposing factors 

 Warm moist weather is conducive for the disease. The disease spread through the rain water. 

Disease cycle 

The pathogen survives in the soil. With the advent of rain the spores will be carried along with the rain droplets causing infection. 

Resistant varieties 

Control 

Biological control: Few bacterial species such as Bacillus lentimorbus, B. cereus and B. pumilus are reported to control the disease. 

Chemical control: Apply 0.2% Bavistin (Carbendazim (50 WP). Completely drench the plants with the fungicidal solution. The leaves can be used for silkworm rearing 7 days after spray. 

Related literature

Chattopadhayay S, Maji MD, Pratheesh Kumar PM, Das KK, Saratchandra B, (2002) Response of mulberry brown leaf spot fungus Myrothecium roridum to different plant extracts.   Int. J. Indust. Entomol.,   5(2): 183-188

Dutta, Ghosh MK, Borah A, Bindroo BB, (2012) Development of Disease Forecasting Model for Leaf rust of Mulberry (Morus alba L.) of Dimapur of North East India.   Nature and Science 2012; 10(8) 66-69.

Govindaiah, Sengupta K, Sharma DD, Gargi, Gunasekhar V, (1989) A  new  leaf  spot  disease  of  mulberry  caused   by  Myrothecium  roridum Tode ex fr.  Curr. Sci., 58(7): 398.

Maji MD, Chattopadhyay S, Pratheesh Kumar PM,  Saratchandra B, (2007) Evaluation of some ethanobotaniclal plant extracts for fungitoxicity against Myrothecium roridum. International J. Industr. Entomol., 14(2): 75-80.

Maji MD, Chattopadhyay S, Pratheesh Kumar PM, Saratchandra B, (2004) Evaluation of mulberry phylloplane bacteria for biocontrol of Myrothecium leaf spot of mulberry caused by Myrothecium roridum.  Agric. Sci. Digest.   24(4): 252-255.

Majumder SK, Bose PC, Banerjee ND, Pratheesh Kumar PM, (2003) Ascorbic acid, an index of fungal infection of mulberry leaf. Sericologia, 43(1): 119-122.

Pratheesh Kumar  PM, Maji MD, Qadri SMH, Saratchandra B, (2009) Bacterial biocontrol agents as alternate fungicides for management of two foliar diseases of mulberry.  Proceedings of the International Conference on Emerging Technologies in Environmental Science and Engineering. Oct. 26-28, Aligarh Muslim University, Aligarh, India. pp 984-991.

Pratheesh Kumar PM,  Qadri  SMH, Pal SC, Saratchandra B, (1999) Evaluation of few fungicides against two leaf spot diseases of mulberry (Morus spp.). Bull. Sericult. Res., 10: 9-15.

Pratheesh Kumar PM, Chattopadhyay S, Maji MD, Raje Urs S, (2005) Severity of foliar diseases of mulberry in West Bengal during commercial crop seasons. Bull. Ind. Acad.  Seric. 9(1):1-6.

Pratheesh Kumar PM, Pal SC, Qadri SMH, (2003). Screening of mulberry germplasm for resistance to leaf spot caused by Myrothecium roridum. J. Mycopathol. Res., 41(1):105-106.

Pratheesh Kumar PM, Qadri SMH, Pal SC, Mishra AK, and Raje Urs S, (2003) Post infection physiobiochemical alteration at various intensities of leaf spot (Myrothecium roridum) in mulberry. International J. Indust. Entomol., 7(2): 175-180.

Teotia RS, Sen SK, (1994) Mulberry diseases in India and their control. Sericologia, 34(1)1-18.